The present invention is directed to a novel grinding aid for forming hydraulic cement powder from clinker raw material and to the method of forming an improved hydraulic cement product.
The term cement is used to designate many different kinds of agents useful to bind materials together. The present invention is directed to hydraulic cements useful to form structural elements, such as those of roads, bridges, buildings and the like. Hydraulic cements are powder material which, when mixed with water, alone or with aggregate, form rock-hard products, such as paste, mortar or concrete. Paste is formed by mixing water with a hydraulic cement. Mortar is formed by mixing a hydraulic cement with small aggregate (e.g. sand) and water. Concrete is formed by mixing a hydraulic cement with small aggregate, large aggregate (e.g. 0.2-1 inch stone) and water. For example, portland cement is a commonly used hydraulic cement material with particular standard specifications established in the various countries of the world (See "Cement Standards of the World", Cembureau, Paris, France). Further, various organizations, such as American Society for Testing and Materials (ASTM), American Association of State Highway and Transportation Officials, as well as other governmental agencies, have established certain minimum standards for hydraulic cements which are based on principal chemical composition requirements of the clinker used to form the cement powder and principal physical property requirements of the final cement mix.
Generally, hydraulic cements are prepared by sintering a mixture of components including calcium carbonate (as limestone), aluminum silicate (as clay or shale), silicon dioxide (as sand), and miscellaneous iron oxides. During the sintering process, chemical reactions take place wherein hardened nodules, commonly called clinkers, are formed. Portland cement clinker is formed by the reaction of calcium oxide with acidic components to give, primarily tricalcium silicate, dicalcium silicate, tricalcium aluminate, and a ferrite solid solution phase approximating tetracalcium aluminoferrite. The conventional cement chemists notation uses the following abbreviations: CaO=C; SiO.sub.2 =S; Al.sub.2 O.sub.3 =A and Fe.sub.2 O.sub.3 =F. Thus, tricalcium silicate=C.sub.3 S; dicalcium silicate=C.sub.2 S; tricalcium aluminate=C.sub.3 A; and tetracalcium aluminoferrite=C.sub.4 AF.
After the clinker has cooled, it is then pulverized together with a small amount of gypsum (calcium sulfate) in a finish grinding mill to provide a fine, homogeneous powdery product. In certain instances other materials may be added or the clinker composition may be modified to provide a particular desired type of hydraulic cement. For example, in certain instances limestone, granulated blast furnace slag, pozzolans and the like are substituted for a portion of the expensive clinker material. These materials are generally inert and are used in cements where economy is of prime consideration and some diminuation in strength is acceptable. The term "blended cement" refers to hydraulic cements having between 5 and 80% (more conventionally 5-60%) clinker substitute material as part of its composition. Other hydraulic cements include, for example, moderate heat portland cement, fly ash portland cement, portland blast furnace cement and the like.
Due to the extreme hardness of the clinkers, a large amount of energy is required to properly mill them into a suitable powder form. Energy requirements for finish grinding can vary from about 33 to 77 kWh/ton depending upon the nature of the clinker. Several materials such as glycols, alkanolamines, aromatic acetates, etc., have been shown to reduce the amount of energy required and thereby improve the efficiency of the grinding of the hard clinkers. These materials, commonly known as grinding aids, are processing additives which are introduced into the mill in small dosages and interground with the clinker to attain a uniform powdery mixture.
One of the major classes of grinding aids used today is the oligomers of lower alkylene glycols, such as diethylene glycol. They are used because of their availability and low cost. These glycols have had their grinding effectiveness enhanced by the inclusion of polyglycerols, lower fatty acids and sulfonated lignin (U.S. Pat. No. 4,204,877); unsaturated aliphatic acid and amines (FR 2,337,699); a C.sub.3 aliphatic acid salt and an amine (U.S. Pat. No. 3,615,785); as well as alcohols and amides (U.S. Pat. No. 5,125,976).
Although the time required (and thereby energy consumed) is lessened when clinkers are ground in the presence of glycol grinding aids, the resultant powder cements do not exhibit any beneficial effect over cements formed without such grinding aid.
It would be desirable to be able to form a hydraulic cement powder product having enhanced properties, such as strength, by grinding in the presence of a grinding aid capable of causing an improved product.